Hi
I built the Lorenz V241 https://groupdiy.com/index.php?topic=67386.0 into this enclosure:
With the Back off the thing looks like this: (This is not the pre, but the original Voltmeter):
Tubes are not visible here, they are on the top.
The enclosure is a bit to small to ensure a good distance from power transformer to input circuit, but it is such a beautiful case with a power transformer and good tube sockets for free, so I had to use it.
Everything works beautifully and the sound is great, but I have this strange noise issue.
Noise gets worse when the chassis is closed.
When the back of the chassis is taken off and the electronics have no shield except the cover over the input circuitry you see in the picture on the right.
I have this Noise spectrum with shorted input and 55dB gain on a RME FF400 with +19dB full scale.
Respectable and no problem even with quite sources.
But when I close the enclosure and everything is shielded the noise gets much worse:
How is this possible? The enclosure is metal, not aluminum, does it maybe reflect the power transformer noise back into the sensitive input circuitry? Or is there some ground loop going on here because the backcover takes up a lot of space and redirects ground currents, even though circuit ground is connected to the chassis only at one point.
I searched, but did not find anything that could help in my case...
Thanks.
I built the Lorenz V241 https://groupdiy.com/index.php?topic=67386.0 into this enclosure:
With the Back off the thing looks like this: (This is not the pre, but the original Voltmeter):
Tubes are not visible here, they are on the top.
The enclosure is a bit to small to ensure a good distance from power transformer to input circuit, but it is such a beautiful case with a power transformer and good tube sockets for free, so I had to use it.
Everything works beautifully and the sound is great, but I have this strange noise issue.
Noise gets worse when the chassis is closed.
When the back of the chassis is taken off and the electronics have no shield except the cover over the input circuitry you see in the picture on the right.
I have this Noise spectrum with shorted input and 55dB gain on a RME FF400 with +19dB full scale.
Respectable and no problem even with quite sources.
But when I close the enclosure and everything is shielded the noise gets much worse:
How is this possible? The enclosure is metal, not aluminum, does it maybe reflect the power transformer noise back into the sensitive input circuitry? Or is there some ground loop going on here because the backcover takes up a lot of space and redirects ground currents, even though circuit ground is connected to the chassis only at one point.
I searched, but did not find anything that could help in my case...
Thanks.